If an object fits in with what Alex Shear calls “the three W’s,” then he wants it.

“Wonderful, wacky, wow!” he explains, chattering on a mile a minute about streamline sleds, skates, scooters, surfboards and other old methods of youth transport mostly from the 1950s to the 1970s (with some as far back as the ’30s).

Shear has loaned a very small part of his 100,000-plus item collection of American pop culture to the Children’s Museum of Manhattan for the exhibit called “Sleds, Skates and Scooters.” After being extended several times since its original closing date last September, museum officials insist it will finally close on May 16.

And from the gasoline powered surfboard to several different pairs of moon shoes to a sled made by an aircraft nose-cone manufacturer after its business dried up at the end of World War II, these objects truly are wonderful and wacky and really do inspire the exclaimation wow!

Shear is an Upper West Sider, born and raised in Lancaster, Pa., where his father was a toy distributer. “I never got over those days. This stuff was so cool,” he says, adding, “I never grew up.” And after only one look at his playful objects of desire, you could only say, duh!

At 60, the former designer and merchandiser for J.C. Penney (he calls himself “the Martha Stewart of chain stores – before there was a Martha Stewart.”) has been scouring flea markets and antique shows around the country since 1969. Some 65 pieces of his grand collection are on display at CMOM – the rest rest at several warehouses, barns and other storage areas in Pennsylvania and Westchester. His apartment? “In order to get inside, you have to walk in sideways,” he volunteers.

The biggest piece on display is the gasoline powered surfboard. Designed in 1960 by the L.A.-based Jet Board Corporation, the idea behind the 11-foot long board was to allow surfers to get far enough out to the really big waves without tiring themselves with all the paddling against the current.

Made of aircraft-type aluminum, the 85-pound Jet Board comes with a retractable handle and removeable engine cover. The 6.25 horsepower, single-cylinder jet motor can propel the board as fast as 10 mph and is water cooled. Its gas tank has a two gallon capacity.

“It’s a precurser to the jet ski,” says Shear, who goes on to show off his gasoline-powered roller skates, complete with 40-pound lawn mower engine backpack. That engine is hooked to the rear of the right skate with a flexible drive shaft cable which also holds a throttle and a brake. This prototype, says Shear, was never manufactured. The gas powered pogo stick, Shear says, was pulled from the market over early safety standard concerns.

A number of items deal with the space race, from Astronaut-emblazened metal saucer sleds to toy space helmets. And then, there are the shoes that, says Shear, “simulate zero-gravity.” For years, he continues, there was interest in what it would be like to be on the moon, from designers, writers, and in comics – the whole Buck Rogers thing.

One pair, from the 1950s, is made of metal painted bright red and powered by heavy duty springs. Another pair, allows a kid to walk on a cushion of air. And still another, dubbed trampoline shoes, says Shear, caused trouble because kids – including his own sister – would fall off them with great frequency.

“One of the goals of this exhibit is to generate conversation among grandparents, parents and kids,” says CMOM’s Andy Ackerman.

Looking in on visitors to the exhibit, Ackerman says he hears a lot of, “‘When I was a kid’ – and then it opens up a flood of conversations.

“It’s kind of remarkable when you have the three generations because the child gets to hear about their parents when their parents were kids, through their grandparents. And they love that.

“‘I remember when your father was your age on the sled’ – that’s a common theme.”

The Children’s Museum of Manhattan is at 212 W. 83rd St., between Broadway and Amsterdam. Weekend hours are 10 a.m. to p.m. Admission is $6 (free for families of New York police officers and fire fighters with ID). For more information, call (212) 721-1223.

Fun facts about skateboards

Skateboards first went on sale in 1958, when a California surf shop began mounting skate wheels on wooden boards. But sidewalk surfing really captured the imagination big-time in 1965, when the first National Skateboarding Championship was broadcast on “Wide World of Sports,” and Jan and Dean released the song, “Sidewalk Surfing.” The budding sport also made the cover of Life magazine, with the headline: “The craze and the menace of skateboards.” Inside, Life reported the skateboard was “the most exhilarating and dangerous joy-riding device this side of the hot rod.”